It is known that elongating the growing season for agricultural plant materials will provide an opportunity to increase the ultimate yield from the plant. In some agricultural areas the overall growing season is limited in the early part of the season by frost problems, whether at night or during daytime, that may destroy seedling plant materials. In those areas early planting must wait until the possibilities of frost have passed. Even in those areas that daytime temperatures are high there is still the possibility of nighttime frost, and planting must wait until nighttime frost damage can be avoided. If it were possible to plant earlier in the season and protect the plant from frost, the overall growing season can be extended with the resultant potential for increased yield from the growing plants.
It has been suggested to protect seedling plants by providing coverings for the seedling plants either as entire row covers or individual plant covers. It has also been suggested that individual plant covers may contain fluids that will release stored heat during cold periods to provide protection for the plant materials covered by the plant cover. One such individual plant protector is shown in U.S. Pat. No. 4,267,665 issued to Volney Wallace. That patent suggests a flexible, double walled thermal protective covering for plants wherein the flexible material has inner and outer tubular walls joined to provide compartments for water or the like.
A difficulty has been observed with the plant protectors of the type suggested by the Wallace patent in that those covers are flexible and are not self supporting when not containing a fluid or the like. Plant protectors of the type suggested by Wallace require the use of additional staking to support the protector whether full of fluid or empty. When those flexible containers collapse they have a tendency to smother the plant material or to become imbeded into the soil around the plant. Furthermore, the flexible covers are difficult to empty and to retreive when empty and collapsed on the ground.